In the prior art, a wide variety of shapes have been used to harness the power of air. See, for example, the schematic prior art drawings shown in FIGS. 1A-1D. These shapes are designed primarily to act in response to air flowing in the direction of the arrow identified as "air flow" in FIGS. 1-3, impacting upon the angle of attack at which the airfoil blade is mounted, and causing the blade to lift. In a typical airplane wing (airfoil), for example, the angle of attack is such that a negative pressure is created above the wing (blade or airfoil) and the wing rises as the air flows across it.
In my prior art U.S. Pat. No. 4,655,122, I disclosed an improved aerodynamic shape which comprised essentially a planar face portion and leading and trailing edges associated with opposing ends of the face portion in a pan-shaped enclosure shown more particularly in the detailed cross section of FIG. 4 of that patent. This blade was shown in use in an air damper where one or more blades were pivoted for rotation within a frame. In that environment, the blades provided an increased lift when forced to open by escaping air from a structure, and thus this permitted the blades to be constructed of a relatively heavy gauge material without compromising damper efficiency. The air flow patterns and dimensions are also disclosed in detail.
Also in the prior art, it was known to use windmills with air compressor units that are powered by the wind energy turning the windmill, to store air under pressure for use, for example, in generating electricity. See, for example, U.S. Pat. Nos. 4,055,950; 4,236,083 and 4,447,738.
Windmill type designs have also been used in wind turbines with various shaped impeller blades disposed at various angles and encased in a cowling designed to direct the wind over the blades. See, for example, U.S. Pat. Nos. 1,025,428; 4,021,135; 4,140,433; 4,132,499; 4,133,992; 4,324,985 and 4,720,640.
One of the primary goals of the prior art windmill configurations was to get more revolutions per minute (rpm) out of the device at lower wind speeds and more power at similar rpm. Thus, the blade configurations were such as to pass air quickly through the device. To do this, the blades would be so configured and positioned for maximum power and not to interfere with each other's air flow.
One of the problems with prior art windmill devices was that in sustained high winds they would tend to "run away" and break up. Furthermore, at low winds or intermittent winds, they could not produce the sustained energy, i.e., constant speed, necessary to produce, for example, electricity.
In my work with windmills, I experimented with various shaped blades, such as that disclosed in my U.S. Pat. No. 5,599,172, for a wind energy conversion system. Therein, I disclosed a new wind energy conversion system for particular application to stored energy, such as compressed air. In accordance with my invention, energy was extracted from the air movement at low speeds. The configuration and spacing of the blades and the shaping of the device which supports them was such that there was a minimum negative interaction between adjacent blades to provide more torque at slower speeds. In accordance with my device, I collected as much air as possible within the device, and thus I collected as much force as possible. Further, the shape, positioning and configuration of the blades within the device tended to prevent it from running away; in other words, there was actually a rotary speed limiting effect.
It became apparent to me that the preferred blade structure had characteristics which were not known in the prior art.